1. Field of the Invention
The invention concerns improved trick mode playback, and more particularly to providing user flexibility in selecting a variable speed trick mode.
2. Description of the Related Art
The introduction of disks recorded with digitally compressed audio and video signals, for example, utilizing MPEG compression protocols, can provide sound and picture quality that is virtually indistinguishable from the original material. However, users will expect such digital video disks (DVDs) to offer, at a minimum, features similar to those of predecessor devices such as an analog videocassette recorder (VCR). For example, a DVD can be expected to provide playback in either forward or reverse directions at speeds slower or faster than a normal playback speed, designated 1xc3x97 by convention. Such non-standard speed playback features are known as trick modes.
Providing trick mode features for MPEG encoded video signals can be challenging due to the hierarchical nature of the compression algorithms that are used to form pictures having varying degrees of compression into groups. These groups are termed groups of pictures (GOPs) and can require sequential decoding. Within this disclosure, a GOP can be extended to include a structure between two successive intra-coded pictures plus one of the intra-coded pictures. A detailed description of the MPEG 2 standard is published as ISO/IEC Standard 13818-2.
Notwithstanding, an MPEG 2 signal stream can comprise three types of pictures having varying degrees of content compression. An intra-coded picture (I-picture) has the least compression of the three types and can be decoded without reference to any other picture. A predictive picture (P-picture) can be compressed with reference to a preceding I-picture or P-picture and the P-picture can achieve a greater degree of compression than an I-picture. The third type of MPEG picture, termed a bi-directionally predictive picture (B-picture), can be compressed based on predictions from preceding and/or succeeding I or P pictures. B-pictures can have the greatest degree of compression. The three types of MPEG pictures can be arranged to form GOPs.
FIG. 1 depicts an exemplary GOP 55 within an MPEG display sequence 50. Referring to FIG. 1, GOP 55 can contain 12 consecutive pictures within the MPEG display sequence 50. Since only an I-picture is decodable without reference to any other picture, each GOP can only be decoded following the decoding of an I-picture. The first P-picture can be decoded and stored based on the stored preceding I-picture. The prediction of a P-picture based on the preceding I-picture is indicated by 62. Subsequent P-pictures can be predicted from the preceding P-picture. The prediction of a P-picture based on the preceding P-picture is indicated by 60 and 68. Finally, B-pictures can be decoded by means of predictions from preceding and/or succeeding reference pictures, for example, stored P-pictures. Exemplary predictions of a B-picture from a preceding P-picture are 64 and 70. Exemplary predictions of a B-picture from a succeeding P-picture are 66 and 72.
The hierarchical nature of the coded pictures comprising MPEG groups of pictures necessitate that the I-pictures and P-pictures of each GOP are decoded in the forward direction. In the forward direction, playback typically occurs sequentially although pictures can be skipped or added to achieve a desired playback speed. Importantly, in the reverse mode, features can be provided by effectively jumping back to an earlier or preceding I-picture and then decoding in a forward direction through the GOP corresponding to that I-picture. The decoded pictures can be stored in frame buffer memories for subsequent read out in a reverse direction to achieve a desired reverse program sequence.
To provide visually smooth reproduction during trick modes, timely disk retrieval and access to specific pictures from memory can be required. Although each digital disk can be encoded with navigation data that provides picture access points, these are limited in number, and may inherently contribute to temporally aliased image motion. In order to achieve temporally smooth trick mode reproduction at varying speeds in forward and reverse directions, it can be necessary to provide access to, and decoding of all encoded pictures. This can require vast amounts of high-speed memory and where such memory is unavailable, the buffers can be overrun resulting in loss of pictures and degradation in performance. Thus, a need exists for improved trick mode performance without relying entirely on vast amounts of high-speed memory and processing power.
Although a playback device can have a locally associated decoder, a remotely located decoder arrangement is also possible. For example, a playback device can include an integrated decoder. However, a display device placed at a location remote from the playback device can also have its own decoder. In this regard, the decoder associated with the display device can be called a remote decoder. In remote decoder arrangements, it can be very difficult to perform trick modes. Oftentimes, a trick mode involves skipping a number of pictures in a video signal such as during a fast motion trick mode. Skipping pictures in a video signal being transmitted to a remote decoder can actually increase the average bit rate of the signal. Since the bandwidth between the digital video recorder or player and the remotely located decoder is generally limited, performing a fast motion trick mode may cause the signal to exceed the maximum bit rate of the transmission channel.
The invention provides a method and system for implementing a selectable variable trick mode playback speed for playback of a compressed video presentation stored on a storage medium. A user can select the selectable variable trick mode. The method can include, in response to a command for trick mode playback of a portion of the video presentation, determining a display time for displaying a segment of the portion of the video presentation at the selected variable trick mode speed. Subsequently, a selection of the pictures to be deleted from the segment can be made in order to achieve the determined trick mode display time during the playback of the portion of the video presentation at the selected variable trick mode speed. The selected pictures can subsequently be deleted. The trick mode display time can represent the time required for displaying the pictures in the segment of the video presentation at the selected variable trick mode playback speed.
In accordance with the inventive arrangements, the step of determining the display time for the segment at the selected variable trick mode speed can further include the step of determining a display time required for displaying the segment at a normal playback speed of 1xc3x97. Subsequent to determining the display time required for displaying the pictures in the segment at the selected variable trick mode speed, the display time for the segment can be adjusted to ensure that it is an integer number of field display periods. A residual portion remaining from adjusting the display time for the segment can be added to a trick mode display time for a segment of the video presentation that will subsequently be displayed during playback at the selected variable trick mode speed. The subsequent segment can be a remaining portion of the pictures in an existing segment or another segment of the video presentation. The command for trick mode playback of the portion of the video presentation can be a forward trick mode command.
The method can further include the step of displaying a remaining portion of the pictures resulting from deletion of the determined pictures from the segment, the remaining pictures being displayed at the selected variable trick mode speed. The segment of the video presentation can be a group of pictures or any other suitable grouping or categorization of the pictures. In determining or selecting which pictures can be deleted the lowest priority pictures can be selected first. Additional lowest priority pictures can be replaced with dummy pictures if the available bandwidth would be exceeded when the lowest priority pictures can be deleted from the segment. Advantageously, the dummy pictures can preferably be distributed evenly throughout the segment. The method can further include the step of decoding at least a portion of the segment of the portion of the video presentation with a remote decoder, and the command for trick mode playback can be a fast trick mode playback command.
In a further aspect of the invention, a system for implementing a selectable variable trick mode playback speed for playback of a compressed video presentation stored on a storage medium is provided. A user can select the selectable variable trick mode speed. The system can include means for determining a display time for displaying a segment of a portion of the video presentation at the selected variable trick mode speed. The determining means can be configured to respond to a command for trick mode playback of the portion of the video presentation. Additionally, the system can also provide means for selecting which pictures are to be deleted from the segment to achieve the determined trick mode display time during the playback of the segment of the video presentation at the selected variable trick mode speed. The system can also provide means for deleting those pictures selected for deletion. The means for determining the display time for the segment at the selected variable trick mode speed can further comprise means for determining a display time required for displaying the segment at a normal playback speed.
In accordance with the inventive arrangements, the means for determining the display time for the segment at the selected variable trick mode speed can further include means for adjusting the display time for the segment to an integer number of field display periods. The system can further include means for adding a residual portion of the display time remaining from the adjusted display time for the segment to a trick mode display time for a subsequently displayed segment of the portion of the video presentation played back at the selected variable trick mode speed. The trick mode playback can be a forward playback trick mode, although the invention is not limited in this regard. The system can further include means for displaying a remaining portion of the pictures resulting from the deletion of the pictures from the segment. Notably, the segment can be a group of pictures. In this regard, the display means can display the remaining pictures at the selected variable fast trick mode speed.
The means for selecting those pictures that are to be deleted from the segment can further include means for determining which pictures are to be deleted based on a priority of the pictures. The selecting means can further include means for selecting those pictures having lowest priority within segment or group of pictures. The system can further include means for replacing additional lowest priority pictures with dummy pictures if the available bandwidth of the channel would be exceeded when the lowest priority pictures are deleted from the segment. Preferably, the dummy pictures can be evenly distributed throughout the segment. The system can further include a remote decoder for decoding at least a portion of the segment of the portion of the video presentation with a remote decoder, and the command for trick mode playback can be a fast trick mode playback command.
In a further aspect of the invention, a method for implementing a selectable variable trick mode playback speed for playback of a compressed video presentation stored on a storage medium is provided. The method can include, responsive to a command for trick mode playback of a portion of the video presentation, determining a display time for displaying a segment of the portion of the video presentation at the selected variable trick mode speed. Pictures can be selected to be repeated from the segment to achieve the determined display time during the playback of the portion of the video presentation at the selected variable trick mode speed. Notably, the selected pictures can be repeated. The command can be a forward trick mode command.
The step of determining the display time for the segment at the selected variable trick mode speed can further include the step of determining a display time required for displaying the segment at a normal playback speed. To determine the display time for the segment at the selected variable trick mode speed, the display time for the segment can be adjusted to an integer number of field display periods.
Moreover, a residual portion remaining from the adjusted display time for the segment can be added to a trick mode display time for a subsequently displayed segment of the portion of the video presentation played back at the selected variable trick mode speed. The method can further include the step of displaying a remaining portion of the pictures resulting from repetition of the determined pictures from the segment. Importantly, these remaining pictures can be displayed at the selected variable trick mode speed.
The segment of the video presentation can be a group of pictures. A picture priority can be used to determine those pictures in a segment that are to be repeated. In this regard, the step of selecting which pictures are to be repeated from the segment can further include the step of selecting pictures having highest priority within a segment. The method can further include the step of decoding at least a portion of the segment of the portion of the video presentation with a remote decoder, and the command for trick mode playback can be a slow trick mode playback command.
The invention further provides a system for implementing a selectable variable trick mode playback speed for playback of a compressed video presentation stored on a storage medium. The system can include means for determining a display time for displaying a segment of a portion of the video presentation at the selected variable trick mode speed. The means for determining the display time can be responsive to a command for trick mode playback of the portion of the video presentation. The command can be a forward trick mode command. Selecting means can be provided for selecting which pictures are to be repeated from the segment to achieve the determined trick mode display time during the playback of the portion of the video presentation at the selected variable trick mode speed. Repeating means can be provided for repeating the selected pictures.
The means for determining the display time for the segment at the selected variable trick mode speed can further include means for determining a display time required for displaying the segment at a normal playback speed. The means for determining the display time for the segment at the selected variable trick mode speed can further include means for adjusting the display time for the segment to an integer number of field display periods. The system can further include means for adding a residual portion remaining from the adjusted display time for the segment to a trick mode display time for a subsequently displayed segment of the portion of the video presentation played back at the selected variable trick mode speed.
Display means can be provided for displaying a remaining portion of the pictures resulting from repetition of selected pictures from the segment. The segment of the video presentation can be a group of pictures. The display means can display the remaining pictures at the selected variable trick mode speed. The selecting means can further include means for determining which pictures are to be repeated based on a priority of the pictures. In this regard, the selecting means can further include means for selecting pictures having highest priority within the segment. The system can further include a remote decoder for decoding at least a portion of the segment of the portion of the video presentation, and the command for trick mode playback can be a slow trick mode playback command.